1. Field of the Invention
This invention relates generally to rotary seals for establishing sealing between a rotary element and a static element for lubricant retention and environment exclusion. More particularly the present invention relates to resilient rotary shaft seals suitable for hydrodynamically lubricating the dynamic sealing interface between a resilient sealing element and a relatively rotatable surface and having means for restricting and diverting lubricant for the purpose of enhancing lubricant film thickness in the sealing interface and causing lubricant movement toward the environment for interface flushing activity and for ensuring adequate lubrication of the entire dynamic sealing surface.
2. Description of Prior Art
Hydrodynamically lubricated rotary shaft seals marketed by Kalsi Engineering, Inc. of Sugar Land, Tex. under the registered trademark "Kalsi Seals" are used for lubricant retention and environment exclusion. FIG. 1 represents prior art constructed in accordance with the principles of U.S. Pat. Nos. 4,610,319 and 5,230,520 commonly assigned herewith and described herein to convey the distinction between prior art and the present invention. FIG. 1 is a cross-sectional view representing the uncompressed cross-sectional shape of ring shaped, resilient interference-type prior art hydrodynamic seal 2 configured for sealing against a relatively rotatable surface (not shown) of cylindrical form. In service, hydrodynamic seal 2 is installed in a circular seal groove (not shown) and compressed between a groove counter-surface and a relatively rotatable surface and used to separate a lubricant from an environment. From an overall orientation standpoint, surface 18 is oriented toward the lubricant, and surface 20 is oriented toward the environment. Surface 20 is positioned so that circular dynamic sealing lip 24 is largely supported by an environment side groove wall to help resist extrusion.
When hydrodynamic seal 2 is installed in a circular seal groove, static sealing surface 40 of circular protruding static sealing lip 22 is compressed against a cylindrical groove counter-surface. The protruding circular dynamic sealing lip 24 defines dynamic sealing surface 26 which is compressed against the relatively rotatable surface. The circular seal groove is sized to hold hydrodynamic seal 2 in compression against the relatively rotatable surface, thereby initiating a sealing relationship with the groove counter-surface and the relatively rotatable surface. When relative rotation occurs between the circular seal groove and the relatively rotatable surface, hydrodynamic seal 2 remains stationary with respect to the groove counter-surface maintaining a static sealing relationship therewith, while the interface between the circular dynamic sealing lip 24 and the relatively rotatable surface becomes a dynamic sealing interface. The lubricant side of circular dynamic sealing lip 24 has a gradually converging relationship with the relatively rotatable surface a result of hydrodynamic inlet 32 which is tangent to lubricant-side 30 at tangency location 68 and to dynamic sealing surface 26 at tangency location 70. Tangency location 68 and tangency location 70 are represented by dashed lines which show the limits of hydrodynamic inlet 32. For illustrative purposes, the relative rotation direction is assumed to be in the direction depicted by arrow 42. Relative to the relative rotation direction 42, each of the waves 44 of dynamic sealing surface 26 have a leading edge 46 and trailing edge 48. Hydrodynamic inlet 32 positionally varys in a wavy pattern relative to the relative rotation direction 42 as a result of being tangent to wavy lubricant-side 30. Hydrodynamic inlet 32 is a simple longitudinally oriented radius which is the same size on both the leading edge 46 and trailing edge 48.
Interrelation of the circular exclusionary geometry 34 and wavy lubricant-side 30 of circular dynamic sealing lip 24 provides dynamic sealing surface 26 with a varying width, including maximum width 28A and minimum width 28B which causes dynamic sealing surface 26 to have a series of waves 44. Width 38 of static sealing surface 40 is approximately the same as the average of 28A and 28B to provide approximate compressive symmetry to minimize compression-induced seal twisting.
In response to relative rotation between hydrodynamic seal 2 and the relatively rotatable surface, the positionally varying, gradually converging relationship between the lubricant side of circular dynamic sealing lip 24 and the relatively rotatable surface generates a hydrodynamic wedging action which introduces a lubricant film between the dynamic sealing surface 26 and the relatively rotatable surface and in the process produces minute lubricant leakage into the environment.
Abrupt circular exclusionary geometry 34 produces a local increase in interfacial contact pressure in the dynamic sealing interface between dynamic sealing surface 26 and the relatively rotatable surface and does not generate a hydrodynamic wedging action, thereby excluding the environment from the dynamic sealing interface.